There's the FOMBA trails near Lake Massabesic. Check out the website for a trail map and directions.
www.fomba.com. Lot's of New England style single track with rocks and roots and fireroads. It's one of my favorite places to ride
There's also Bear Brook State Park in Allenstown which is about 20-30 minutes from Manchester. I rode there today and the trails are in awesome shape. Studs would be helpful. Bear Brook has miles and miles of trails. Fireroads, single track, climbing, etc. It's got everything XC. This IS my favorite place to ride. You can get a downloadable trail map here.
http://www.snemba.org/trails.html
A guide would be helpful here to show you a few good routes. Post up when you'll be around and I'm sure there will be people willing to show you around. I would.
Hope this helps you out some. Let me know if you have any more questions.
JP